The present invention relates to a method of controlling the flow rate of air intake of an internal combustion engine, particularly during idling or deceleration.
There is known a method of controlling air intake of an internal combustion engine when a throttle valve disposed in an intake passage is at the fully closed position. According to this conventional method, the flow rate of intake air, when the throttle valve is fully closed, is controlled by adjusting a control valve disposed in an air bypass passage which interconnects the intake passage at a position located upstream of the throttle valve with the intake passage at a position located downstream of the throttle valve. Such an air intake control method is usually employed for controlling the idling rotational speed of the engine. The idling rotational speed can be controlled by a closed loop if the bypass control valve is adjusted to control the flow rate of the air sucked into the engine through the bypass passage so that the detected actual rotational speed of the engine becomes equal to the desired idling rotational speed.
The desired rotational speed is usually changed depending upon the change of the operating condition of the engine and/or upon the change of the load condition of the engine. In this case, the change of the operating condition corresponds to, for example, the change of the coolant temperature of the engine, the position of a starter switch, and/or the change of the position of the throttle valve. Furthermore, the change of the load condition corresponds to the on-off switching of an air conditioner, and/or the change of the shift position of an automatic transmission from the neutral range or the parking range (these ranges are hereinafter referred to as the N range) to the drive range (hereinafter referred to as the D range) and vice versa.
However, according to the conventional control method, since the desired rotational speed is changed abruptly in response to the change of the operating condition and/or of the load condition, the actual rotational speed which is controlled, by the closed loop control, depending upon the difference from the desired rotational speed cannot respond to the changed desired rotational speed. Therefore, when the desired rotational speed changes, overshooting or hunting occurs in the controlled actual rotational speed. Thus, according to the conventional technique, the controlled actual rotational speed cannot be smoothly and quickly converged to the changed desired rotational speed, spoiling the smooth driving feeling an operator might have.